Throughout this application, various publications are referenced in Arabic numerals in parentheses. Full text citations of these publications can be found at the end of the specification, immediately preceding the claims. The disclosures of these publications in their entirety are hereby incorporated by reference into this application in order to more fully describe the state of the art as known to those skilled therein as of the date of the invention described and claimed herein.
The pyridine C-nucleoside having the structure: ##STR2## which is isosteric to nicotinamide riboside, was synthesized by these inventors [Kabat, Pankiewicz, Watanabe, J. Med. Chem., 1987, 30, 924-927; Kabat et al., Chem. Pharm. Bull., 1988, 36, 634-640; Pankiewicz et al., J. Org. Chem., 1988, 53, 3473-3479] in the hope that such an analogue may be converted biologically into the corresponding nicotinamide adenine dinucleotide, NAD coenzyme, analog having the structure: ##STR3## and exert biological activities. The non-charged NAD isostere, Compound 2, which is incapable of participating in biological oxidation-reduction process(es) may inhibit the NAD-dependent enzyme, IMP-dehydrogenase, and may induce anticancer activity by blocking the de novo GMP synthesis.
The NAD analog (Compound 2) which contains the C-nucleoside (Compound 1), was found to be a general competitive inhibitor (with respect to NAD) of various dehydrogenases such as inosine monophosphate dehydrogenase (IMPDH), glutamate dehydrogenase (GDH), lactate dehydrogenase (LDH) and malate dehydrogenase (MDH). Interestingly, the NAD analogue (Compound 2) exhibited highly potent and selective inhibitory activity against alcohol dehydrogenase from horse liver.
The present invention relates to the novel class of NAD analogs which contain the nicotinamide, picolinamide or isonicotinamide C-nucleoside in place of nicotinamide riboside. The compounds of this invention have the pyrophosphate (--P--O--P--) bridge connecting the nucleosides or, alternatively, can have a methylene diphosphonate (--P--CH.sub.2 --P--), or difluoromethylene diphosphonate (--P--CF.sub.2 --P--) group as the bridge.
Analogues that contain a methylene diphosphonate (--P--CH.sub.2 --P--) or difluoromethylene diphosphonate (--P--CF.sub.2 --P--) group in place of the pyrophosphate (--P--O--P--) bridge are resistant to enzymic hydrolysis to their corresponding nucleoside 5'-monophosphates. The 2'-fluoroinated adenosine analogues cannot be converted into the corresponding NADP analogues. Such analogues, therefore, cannot interfere with NADP dependent enzymes. In addition, fluorine substituted NAD analogues, as more lipophilic than their corresponding hydroxyl or pyrophosphate groups containing counterparts, could penetrate biological membranes and may better fit to the hydrophobic binding pocket of dehydrogenases.
The compositions of this invention are useful as potent inhibitors of various dehydrogenases of eucaryotic and procaryotic origin. These compounds may also be utilized as therapeutic agents exhibiting anticancer and antiviral activity.
Thiazole-4-carboxamide adenine dinucleotide (TAD) is the active metabolite of the oncolytic C-nucleoside, 2-(.beta.-D-ribofuranosyl)thiazole-4-carboxamide (Tiazofurin, TR). TAD, an analogue of nicotinamide adenine dinucleotide (NAD), was found to be a potent inhibitor of inosine monophosphate dehydrogenase (IMPDH), the key enzyme in the de novo GTP biosynthesis and an important target in anticancer chemotherapy.(2-13) TAD mimics NAD but cannot function as the coenzyme. It has been discovered (14) recently that human IMPDH exists as two isoforms, type I and type II. In normal cells type I is the predominant isoenzyme while type II is selectively up-regulated in neoplastic cells and emerges as the dominant species. (15,16)
The goal in searching for antitumor agents based on IMPDH inhibition is, therefore, to develop a compound which would not affect numerous cellular dehydrogenases but would act as a selective inhibitor of IMPDH--type II.